Morpho-Physiological Response of Oryza glaberrima to Gradual Soil Drying

Soil drought occurrence during dry season has been the main constraint, besides prolonged flooding during rainy season, in increasing cropping intensity and rice productivity in tropical riparian wetland. Use of drought tolerant rice genotype might be a suitable option for overcoming such problem. This study focused on the effects of gradual soil drying during early vegetative growth stage on morphological and physiological traits of five Oryza glaberrima genotypes, namely RAM12, RAM14, RAM59, RAM97 and RAM101, and two Oryza sativa subsp japonica genotypes, i.e. Koshihikari and Minamihatamochi. The plants were subjected to 6 d of gradual soil drying condition from 15 days after transplanting(DAT) to 20 DAT, and were allowed to recover until 22 DAT. Gradual soil drying reduced plant growth as indicated by dry mass accumulation. Drought reduced stomatal conductance and increased leaf rolling score of all the genotypes. All the genotypes showed comparable response on stomatal conductance, but O. glaberrima genotypes performed higher in leaf rolling recovery. Meanwhile, O. sativa genotypes decreased total leaf area and specific leaf area, but increased specific leaf weight in order to avoid further damages due to drought stress. Drought tolerance mechanisms in RAM101, RAM12, RAM59 and RAM14 were associated with leaf morpho-physiological responses, root traits and dry biomass accumulation.

Development of Hydropriming Techniques for Sowing Seeds of Upland Rice in Uganda

Hydropriming is one of the presoaking, seed priming technique that allows seeds to imbibe water and go through the first stage of germination but does not allow radicle appearance. After water imbibition, seeds are dried to their original weight. This technique is used to help crops overcome environment stress. This study aims to assess the morphological traits of farmer’s seeds for developing priming treatments so as to develop appropriate methods to maximize the effect of hydropriming. We collected farmer’s samples of rice sowing seeds grown indifferent regions of Ugandan. For each sample, distribution of the seed density in percentages was calculated. Secondly, germination tests as per seed density levels and as per farmer’s seed samples were conducted for deciding appropriate priming treatment. Finally, wooden boxes experiment was conducted to confirm priming effects. As the result, it was observed that the difference in seed density levels affects the quality of farmer’s seeds, as observed in the case of NERICA4. If the radicle appears during soaking period, the newly developed radicle dies during the seed drying process in the hydropriming treatment. Seed germination was observed after 24 h of sowing at room temperature, even at a seed density level of 1.17, which is vigorous for germination. Consequently, farmer’s seeds were soaked for 24 h to promote water absorption and activate metabolic pathways and to avoid germination failure when seeds are dried to their initial weight. After hydropriming treatment, plant growth was improved. Alternatively, significant difference was not observed in the mean emergence time between hydroprimed and unprimed seeds. These results suggest that priming the seeds by soaking for 24 h and drying to their initial weight considerably affects initial growth after emergence under dry soil condition.